There have been known power transmitting apparatus of a type which, through a combination of sun, planetary and ring gears, can switch between a power-transmitting mode and a non-power-transmitting mode.
FIGS. 12 and 13 are views showing such a power transmitting apparatus disclosed in Japanese Utility Model Publication No. SHO-60-40931 (hereinafter referred to as “patent document 1”). As shown, the disclosed power transmitting apparatus 200 includes a vertical input shaft 201, a sun gear 202 provided on an lower end portion of the input shaft 201, and three planetary gears 203 meshing with the sun gear 202. The power transmitting apparatus 200 further includes a gear support member 204 disposed beneath the planetary gears 203 for supporting thereon the planetary gears 203, an output shaft 205 extending downward from the gear support member 204 in axial alignment with the input shaft 201, and a ring gear 206 surrounding and meshing with the planetary gears 203. The power transmitting apparatus 200 also includes a casing 207 supporting therein the gear support member 204, output shaft 205 and ring gear 206, and a brake unit 208 interposed between the casing 207 and the ring gear 206 for braking the ring gear 206 as instructed by a human operator. When the brake unit 208 is in the braking state, power input via the input shaft 201 is transmitted to the output shaft 205 with a reduced speed, while, when the brake unit 208 is in the non-braking state to allow the ring gear 206 to run idle, the input power is prevented from being transmitted from the input shaft 201 to the output shaft 205.
Further, in the disclosed power transmitting apparatus 200, lubricating oil 209 is stored to a predetermined level in the casing 207, and a surface level 211 of the lubricating oil 209 is set such that the meshing portions of the planetary gears 203 and ring gear 206 are completely immersed in the oil 209.
Generally, in the power transmitting apparatus of the type as disclosed in the patent document 1, slight power transmission from the input shaft 201 to the output shaft 205 would take place even when the brake unit 208 is in the non-braking state to allow the ring gear 206 to run idle. Such slight power transmission from the input shaft 201 to the output shaft 205 in the non-braking state is commonly called “corotation”. It is known that the corotation occurs due to given force acting to keep the ring gear 206 stationary even when the brake unit 208 has released the ring gear 206 into an idling state. However, because the corotation causes the input power to be transmitted to the output shaft 205 when the input power is not to be transmission to the output shaft 205, it is an unwanted phenomenon for the power transmitting apparatus 200 which should be minimized.
Further, in the conventional power transmitting apparatus 200, the gear support 204 can not always rotate in a stabilized manner because it is substantially triangular in shape and supported at the center of the casing 207.